Title:	Quantum Fields from Casual Order
Authors:	Mathur, Abhishek
Thesis Advisor:	Surya, Sumati
Subject:	Theoretical Physics
Issue Date:	Feb-2023
Publisher:	Raman Research Institute
Citation:	Ph.D. Thesis, Jawaharlal Nehru University, New Delhi, 2023
Abstract:	Quantum Field Theory (QFT) in curved spacetime describes physical phenomena in a regime where quantum fields interact with the classical gravitational field. These conditions are generally satisfied either in the vicinity of a black hole or in the post Planckian very early universe. The standard approach to QFT relies heavily on the Poincare symmetry of Minkowski spacetime as a guide to a particular choice of mode expansion and therefore a preferred choice of vacuum. In contrast, in a generic curved spacetime which does not have any symmetry, the choice of mode expansion and hence the vacuum is arbitrary. This suggests that the notion of vacuum and particles is subsidiary. This is the approach taken in algebraic QFT (AQFT), where the primary role is played by the algebra of observables and the choice of state, which is primarily defined as a complex function on this algebra, is relegated to a choice of the representation of this algebra, and is therefore not unique. It is natural to ask if there exists an alternative formulation of the QFT vacuum which is inherently covariant. One such formalism was developed by Sorkin [1] and Johnston [2] called the Sorkin-Johnston (SJ) vacuum. In this thesis we will explore various aspects of the SJ vacuum both in the continuumand in the causal set theory. QFT also plays an important role in understanding the entropy of black holes and other horizons. Entanglement entropy of quantum fields has been proposed as a candidate for these entropies. The standard formulation of the entanglement entropy is given by the von Neumann entropy formula, which requires the QFT states to be defined on a Cauchy hypersurface and is therefore dependent on the choice of the hypersurface. Sorkin, in his 2014 paper [3], proposed a spacetime formulation of the entanglement entropy, which is covariant.
Description:	Restricted Access
URI:	http://hdl.handle.net/2289/8054
Copyright:	This thesis is posted here with the permission of the author. Personal use of this material is permitted. Any other use requires prior permission of the author. By choosing to view this document, you agree to all provisions of the copyright laws protecting it.
Appears in Collections:	Theses (TP)

Items in RRI Digital Repository are protected by copyright, with all rights reserved, unless otherwise indicated.